Cracks in Bjork-Shirley heart valves lead to the death of many patients. Only X-ray technique showed limited success for the detection of fractures in implanted valves. We propose to use a magnetic technique which is non-destructive and non- invasive for crack detection in implanted valves. We will apply in ac magnetic field to the implanted valves and detect the response from the valves with a Superconducting Quantum Interference Device (SQUID), the most sensitive magnetic field sensors. We will monitor the phase shift between the detected signal and the applied field. The resistance for a cracked valve will be different from an intact one, and will introduce dramatic differences in the corresponding phase shift. Preliminary tests at Quantum Magnetics have demonstrated this detection principle on samples simulating intact and broken outlet struts. In Phase I research we will modify our existing instrument to study replacement valves in salt water, in a model of a human body, and also inside live sheep, assisted technically by Shiley Research Center. We will characterize the signals from different size valves and different fractures under various environments. In Phase II we will design, build and test a complete system for the inspection of replacement valves. PROPOSED COMMERCIAL APPLICATION: The proposed research will produce an effective tool for the non-invasive inspection of patients with artificial heart valves. Approximately 50,000 people receive artificial heart valves in the USA each year. The commercial market for this instrument is very large.